NO163623B - CROSS-BINDABLE CARBOXYMETHYL HYDROXYETYL CELLULOSE. - Google Patents

Description

The present invention relates to water-soluble, crosslinkable carboxymethylhydroxyethyl cellulose. In particular, it concerns carboxymethylhydroxyethyl cellulose which, when cross-linked by means of aluminum ion from a suitable source in an aqueous solution, is free from dilution when used in environments at temperatures less than approx. 93°C.

It is known in this art that gels with desirable viscoelastic properties can be prepared in aqueous solutions using cross-linked carboxymethylhydroxyethyl cellulose, hereinafter called CMHEC. A significant shortcoming of these gels is that they are temperature sensitive. When the temperature in the cross-linked gel is increased, the viscosity of the gel is reduced in a way that is well known for almost all substances.

Gels containing cross-linked CMHEC are widely used as oil well fracturing fluids. The incorporation of cross-linked CMHEC provides desirable viscosity and suspension power. Because these gels dilute with increasing temperature, problems arise. In order to achieve a desired viscosity far down in the borehole where the temperature can be close to 93°C, a cross-linked gel with a much higher viscosity must be produced at the surface where a typical temperature can be 26°C. It is difficult to achieve sufficiently high flow rates into the well when pumping gels with this high viscosity.

US-PS 3,448,100 describes a method for the production of carboxymethylhydroxyalkyl-mixed celluloses with a carboxymethyl degree of substitution, hereinafter called DS, within the range of approx. 0.2 to approx. 1.0 and a hydroxyalkyl molar substitution, hereafter called MS, within the range of approx. 0.2 to approx.

5. The patent does not address the problem of temperature-sensitive gels containing cross-linked carboxymethylhydroxyalkyl cellulose.

TJS-PS 4 239 629 describes a gel obtained in water by combining carboxymethylhydroxyethyl cellulose with a compound selected from alkali metal and ammonium dichromate. The patent does not address the problem of temperature-sensitive gels based on cross-linked carboxymethylhydroxyethyl cellulose.

As a result, there is therefore a need for a gel containing cross-linked carboxymethylhydroxyethyl cellulose which avoids the dilution problems when used in environments at temperatures below approx. 93" C, problems not described in the references given above.

According to this, the present invention relates to a crosslinkable carboxymethylhydroxyethyl cellulose where the carboxymethylhydroxyethyl cellulose has a carboxymethyl substitution ratio of 0.10 to 0.20 and a hydroxyethyl molar substitution of more than 1.0, and this cellulose is characterized by containing 1 to 5 wt-#, calculated on the carboxymethylhydroxyethyl cellulose, of basic aluminum acetate.

Gels prepared in aqueous solutions from the improved water-soluble CMHEC, cross-linked by means of an aluminum ion, show no significant dilution at temperatures below 93° C. The degree of substitution is the average number of hydroxyl groups substituted in the cellulose per anhydroglucose unit. As a result, carboxymethyl-(DS) is the average number of substituted carboxymethyl groups per cellulosic anhydroglucose unit.

According to the invention, it has been found that when the carboxymethyl (DS) value for the hydroxyethylated carboxymethyl cellulose according to the invention is less than 0.1, there is no significant gel formation in the presence of aluminum ion; and when the carboxymethyl (DS) value is greater than approx. 0.20, gelation will occur, but there is no significant dilution at elevated temperatures. Preferred CMHEC preparations have a carboxymethyl (DS) value of 0.15 to 0.20.

The degree of hydroxyethylation is described in terms of molar substitution. Molar substitution is the average number of moles of reactant that combine with cellulose per anhydroglucose unit. As a result, the hydroxyethyl (MS) value is the average number of moles of hydroxyethyl incorporated per anhydroglucose unit. The hydroxyethylated carboxymethyl cellulose according to the invention must have a hydroxyethyl (MS) value which is sufficient to make the compound water-soluble. This requires a hydroxyethyl (MS) of over 1.0. For the purposes of the invention, there is really no upper limit to the hydroxyethyl (MS) value as long as the polymer remains water soluble. However, it has been found that if the hydroxyethyl (MS) value is too high, the gel strength of the crosslinked polymer is reduced. As a result, for all applications, the hydroxyethyl (MS) value should be less than about 3.5. The best results are found when the hydroxyethyl (MS) value is in the range of 2.0 to 2.5.

The use of ionic agents to cross-link CMHEC is known to those skilled in the art. The amount of the basic aluminum acetate used as crosslinking agent is, as mentioned, within the range 1% to 5% and preferably within the range 2% to 4%, calculated for the non-crosslinked polymer.

The amount of cross-linked CMHEC to be used to increase the viscosity of an aqueous solution will depend on the particular application and will be readily determined by those skilled in the art. In general, the amount of crosslinked CMHEC to be used will be in the range of 0.1 to 2# based on the weight of uncrosslinked CMHEC.

The following examples are to further illustrate the invention. All percentages are on a weight basis, calculated on the weight of the cellulose, unless otherwise stated.

Examples 1 to 14

The carboxymethylhydroxyethyl cellulose in example 6 was produced by the following method: An approx. eight-liter stirred autoclave glass bowl was charged with 64.8 g (0.4 mol) of cotton linters, calculated on a dry weight basis, and 1000 ml of t-butyl alcohol (99.5+*). The bowl was then sealed to the reactor and purged of oxygen, evacuated to 66 cm gauge pressure and then pressurized to 1.4 kg/cm<2> gauge pressure with nitrogen. This vacuum pressure cycle was repeated 5 times after which, by means of a syringe, caustic solution (61.7 g 50* NaOH/73 ml H 2 O) was added to the stirred cellulose slurry under vacuum. The reactor was given another five degassing cycles as above. The alkali cellulose was stirred for 60 minutes at 15-20°C under a pressure of 0.7 kg/cm<2> gauge pressure with nitrogen. A monochloroacetic acid solution (10.4 g MCA/25 ml t-butyl alcohol) was then added via an injection syringe to the slurry under vacuum. After pressurizing to 0.7 kg/cm<2> gauge pressure N2, the reaction was heated to 70°C (approx. 30 minute heating period) and held there for 30 minutes. After cooling to 40°C and evacuation to approx. 50 cm vacuum, 79.0 ethylene oxide, condensed in a Fischer-Porter tube, was added. After pressure loading to 0.7 kg/cm<2> gauge pressure N 2 , the reaction medium was held at 45°C for 60 minutes and then at 80°C for 120 minutes. After cooling to less than 30°C, the reaction mixture was neutralized with 31 ml of HN0 3 (70*) and 5 ml of glacial acetic acid. After filtration, the wet cake was batch washed in acetone and then dehydrated with 99.5% acetone and dried.

Examples 1-5, 7-11 and 12-14 were carried out in an analogous manner except that the amounts of NaOH, monochloroacetic acid and ethylene oxide added were varied to give such carboxymethyl-(DS) and hydroxyethyl-(MS) as indicated in table 1.

The gel stabilities were obtained for each example as follows:

0.2 g of potassium acetate, 0.8 g of polymer and 3.2 g of potassium chloride were dry mixed in a 16 ml wide necked flask. 0.2 g of basic aluminum acetate was added to 100 ml of distilled water in a 150 ml beaker. The contents of the beaker were air-dried for 10 minutes. 150 ml of tap water and the dry-blended mixture were added to a thermos container with stirring at 600 rpm. After 10 minutes, 0.2 ml of glacial acetic acid (potassium acetate and glacial acetic acid buffered to pH 4.5) was added to the thermos. Then 10 ml of the basic aluminum acetate solution was added. The thermos container was put on and the sample heated to 82°C. The torque that occurred at 600 rpm. constant stirring speed was measured with a sensor connected to the thermos container at intervals of approx. 11°C from 26.6°C to 82.2°C. The results are shown in table 1.

Claims (1)

Crosslinkable carboxymethyl hydroxyethyl cellulose where the carboxymethyl hydroxyethyl cellulose has a carboxymethyl substitution degree of 0.10 to 0.20 and a hydroxyethyl molar substitution of over 1.0, characterized in that it contains 1 to 5 weight-*, calculated on the carboxymethyl hydroxyethyl cellulose, of basic aluminum acetate.